Torque improvement investigation of a double rotor permanent magnet motor based on effective utilization of magnetic field coupling

In this paper, a torque improvement method is presented for a double rotor (DR) permanent magnet motor, where the key is to conduct the study based on effective utilization of magnetic field coupling. To facilitate systematic analysis, the magnetomotive force (MMF) and airgap flux density considering magnetic coupling effect are deduced and analysed. It contributes to building the relationships between the output torque caused by magnetic coupling and magnetic field harmonics. By introducing the coupling sensitivity coefficient, the coupling harmonics in the inner and outer airgap magnetic fields are obtained. Then, two coupling harmonic groups are further determined in terms of phase difference and torque contribution, where one of them is required to be enhanced and the other is needed to be reduced. On the basis of this, a comprehensive coupling factor is defined purposely to realise the design and evaluation of the characteristics of coupling harmonic groups. Some motor performances are analysed in details, including the torque, torque ripple, overload capability, and so on. Finally, a prototype motor is manufactured to verify the feasibility of the presented studies of the DR motor.